The present invention relates to a method of controlling an air-fuel ratio for use in an internal combustion engine and an apparatus for controlling the same and, more particularly to a method of controlling an air-fuel ratio for use in an internal combustion engine suitable for an electric spark ignition type gasoline internal combustion engine and an apparatus for controlling the same.
In a method of controlling the air-fuel ratio according to the present invention, a fuel injection amount being supplied into the internal combustion engine is corrected and thereby the air-fuel ratio in an automatic internal combustion engine control system is controlled or corrected.
The present invention relates to a method of controlling an air-fuel ratio for use, in an internal combustion engine and an apparatus for controlling the same, incorporating a plurality of sensors and an electronic control unit which receives signals from various sensors and which controls a fuel injection amount and an air-fuel ratio in the automatic internal combustion engine control system.
In a method of controlling air-fuel ratio for use in an internal combustion engine equipped with a fuel injection and control, system, an air-fuel ratio control method is employed for accurately and appropriately controlling an amount of fuel being supplied by the fuel injection system during various and diverse operational conditions of the internal combustion engine so as to provide good engine operational characteristics, and an air-fuel ratio control apparatus is operated in accordance the above stated air-fuel ratio control method.
A method of controlling air-fuel ratio for use in an electric spark ignition type gasoline internal combustion engine suitable for use in an automobile has a learning function for the air-fuel ratio and apparatus for controlling the same. In a method of controlling air-fuel ratio for use in an automobile, a deviation to a target value of an air-fuel ratio is divided at a predetermined rate in accordance with a parameter indicating an operational condition of the internal combustion engine, and each divided deviation is learned as a distinct element of an engine operational condition parameter.
In a conventional apparatus for controlling air-fuel ratio for use in an internal combustion engine, a fuel injection amount being supplied into the internal combustion engine is determined in accordance with a parameter indicating an operational condition of the internal combustion engine, and an air-fuel ratio is calculated in accordance with a physical amount of an exhaust gas.
The above stated conventional air-fuel ratio control technique in the field of the internal combustion engine will be explained in more detail as follows referring to FIG. 2.
An intake air flow amount Q.sub.a being taken into an electric spark ignition type gasoline internal combustion engine 7 for an automobile is detected with an air flow sensor 3, and a fuel injection amount is determined through an electronic control unit 15. A fuel injector 13 is driven and then fuel is injected into a combustion chamber of the gasoline internal combustion engine 7.
When exhaust gas having been burned in the combustion chamber passes at a position in which an oxygen concentration detecting sensor (O.sub.2 sensor) 19 is provided at a midway portion of an exhaust pipe, and an actual air-fuel ratio is detected through O.sub.2 sensor 19. The electronic control unit 15 adjusts the fuel injection amount in accordance with this detected signal from O.sub.2 sensor 19, thereby an optimum air-fuel ratio for the internal combustion engine 7 may be obtained.
A fuel injection pulse width T.sub.i at this time is determined in the electronic control unit 15 in accordance with the following formulas. EQU T.sub.i =T.sub.p .multidot.K.sub.2 .multidot..alpha.+T.sub.s ( 1) EQU T.sub.p =K.sub.1 .multidot.Q.sub.a /N (2)
wherein K.sub.1 is a constant, Q.sub.a is an intake air flow amount, N is an engine speed, K.sub.2 is a correction coefficient according to an engine cooling water temperature etc., .alpha. is an air-fuel ratio correction coefficient, T.sub.s is a battery voltage correction part, and T.sub.p is a basic fuel injection pulse width.
A feed-back control for controlling the air-fuel ratio through O.sub.2 sensor 19 in the internal combustion engine 7 is carried out by using the air-fuel ratio correction coefficient .alpha. shown in the formula (1).
The air-fuel ratio correction coefficient .alpha. moves so as to inject the fuel injection pulse width T.sub.i with a condition having a theoretical air-fuel ratio being a value of 14.7. When the theoretical air-fuel ratio is a value of 14.7, the air-fuel ratio correction coefficient .alpha. becomes a value of 1.0. When the air-fuel ratio resides at a rich side, the air-fuel ratio correction coefficient .alpha. is smaller than 1.0, and when the air-fuel ratio resides at a lean side, the air-fuel ratio correction coefficient .alpha. is larger than 1.0.
Herein, in case of the air-fuel ratio correction coefficient .alpha.=1.0 or during assembling the air flow sensor 3 or the fuel injector 13 etc. in which no learning for the air-fuel ratio control is carried out, the fuel injection amount being supplied into the internal combustion engine 7 varies due to an individual performance characteristic of the air flow sensor 3, or the fuel injector 13 etc.
Each individual performance dispersion of the apparatus comprising a fuel injection and control system such as the air flow sensor 3 and the fuel injector 13 etc. may absorb momentarily through the change of such an air-fuel ratio correction coefficient .alpha. value in accordance with the feed-back control for the air-fuel ratio in the internal combustion engine 7.
However, when the engine is operating in a low temperature period etc. during an engine operation in which O.sub.2 sensor 19 operates in an unavailable area, or in case the feed-back control for the air-fuel ratio cannot follow conditions due to rapid changes in the operational condition of the internal combustion engine 7, then it is impossible to absorb such individual performance dispersion in the operation of the fuel injection and control apparatuses, such as the air flow sensor 3, the fuel injector 13 etc.
In the automatic control of the air-fuel ratio in the internal combustion engine 7, due to various causes, it is very difficult to have no occurrence of errors, however an actual damage being suffered by those errors may be eliminated through the control or correction of those errors.
Now, the maximum main factors in the errors with regard to the automatic control of the air-fuel ratio in the internal combustion engine 7 are an error in detection through the individual performance dispersion of the air flow sensor 3 and an error in the fuel injection amount through the individual performance dispersion of the fuel injector 13.
For example, the tolerance of the air flow sensor is about .+-.6% and the tolerance of the fuel injector is from about .+-.7.1% to about .+-.4.5%. The total tolerance is from about .+-.13.1% to about .+-.10.5%. Therefore, it is impossible to neglect the individual performance dispersions by the air flow sensor and the fuel injector.
Namely, in the conventional automatic air-fuel ratio control technique, there are problems that when the extent of deviation in the intake air flow amount Q.sub.a and the extent of deviation in the fuel injection amount are changed in accordance with the value of the engine operational condition parameter, no high accuracy of the air-fuel ratio control or correction is obtained.
Further, in the conventional automatic air-fuel ratio control technique, there are no considerations given to a method of the learning for air-fuel ratio control or correction in the electronic control unit and also ways to achieve an early convergence for the air-fuel ratio control or correction.
A conventional air-fuel ratio control technique for use in an internal combustion engine is disclosed, for example, in U.S. Pat. No. 4,726,344, in which an optimum air-fuel ratio in the internal combustion engine is determined in dependence upon renewal of a plurality of learning values related to a plurality of load regions of the internal combustion engine. This air-fuel ratio control technique is arranged to conduct simultaneous learning of the learning values at a frequency in accordance with a lapse of time and to conduct selective learning of the learning values in accordance with a change of the load acting on the internal combustion engine.